Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.94   10.657%   $265.5104   $265.51   $265.50   $265.50  
  Purchase #2 $173.66   7.839%   $187.2732   $187.27   $187.25   $187.30  
  Purchase #3 $86.63   6.190%   $91.9924   $91.99   $92.00   $92.00  
  Purchase #4 $221.69   9.618%   $243.0121   $243.01   $243.00   $243.00  
  Purchase #5 $82.66   13.689%   $93.9753   $93.98   $94.00   $94.00  
  Purchase #6 $79.71   8.472%   $86.463   $86.46   $86.45   $86.50  
  Purchase #7 $102.44   4.239%   $106.7824   $106.78   $106.80   $106.80  
  7 purchase totals = $986.73       $1,075.0088   $1,075.00   $1,075.00   $1,075.10